PCT publication WO 01/45709 published 28 Jun. 2001 discloses calcium channel blockers where a piperidine or piperazine ring links a benzhydril moiety to an additional aromatic moiety or benzhydril. This publication, which is based on parent application Ser. No. 09/476,927, discussed above, is incorporated herein by reference. As explained in these applications, native calcium channels have been classified by their electrophysiological and pharmacological properties as T, L, N, P and Q types. T-type (or low voltage-activated) channels describe a broad class of molecules that transiently activate at negative potentials and are highly sensitive to changes in resting potential. The L, N, P and Q-type channels activate at more positive potentials (high voltage activated) and display diverse kinetics and voltage-dependent properties. There is some overlap in biophysical properties of the high voltage-activated channels, consequently pharmacological profiles are useful to further distinguish them. Whether the Q- and P-type channels are distinct molecular entities is controversial. Several types of calcium conductances do not fall neatly into any of the above categories and there is variability of properties even within a category suggesting that additional calcium channels subtypes remain to be classified.
Biochemical analyses show that neuronal high voltage activated calcium channels are heterooligomeric complexes consisting of three distinct subunits (α1, α2δ and β). The α1 subunit is the major pore-forming subunit and contains the voltage sensor and binding sites for calcium channel antagonists. The mainly extracellular α2 is disulfide-linked to the transmembrane δ subunit and both are derived from the same gene and are proteolytically cleaved in vivo. The β subunit is a nonglycosylated, hydrophilic protein with a high affinity of binding to a cytoplasmic region of the α1 subunit. A fourth subunit, γ, is unique to L-type calcium channels expressed in skeletal muscle T-tubules.
Recently, each of these α1 subtypes has been cloned and expressed, thus permitting more extensive pharmacological studies. These channels have been designated α1A–α1I and α1S and correlated with the subtypes set forth above. α1A channels are of the P/Q type; α1B represents N; α1C, α′1D, α1F and α1S represent L; α1E represents a novel type of calcium conductance, and α1G–α1I represent members of the T-type family.
Further details concerning the function of N-type channels, which are mainly localized to neurons, have been disclosed, for example, in U.S. Pat. No. 5,623,051, the disclosure of which is incorporated herein by reference. As described, N-type channels possess a site for binding syntaxin, a protein anchored in the presynaptic membrane. Blocking this interaction also blocks the presynaptic response to calcium influx. Thus, compounds that block the interaction between syntaxin and this binding site would be useful in neural protection and analgesia. Such compounds have the added advantage of enhanced specificity for presynaptic calcium channel effects.
U.S. Pat. No. 5,646,149 describes calcium channel antagonists of the formula A-Y-B wherein B contains a piperazine or piperidine ring directly linked to Y. An essential component of these molecules is represented by A, which must be an antioxidant; the piperazine or piperidine itself is said to be important. The exemplified compounds contain a benzhydril substituent, based on known calcium channel blockers (see below). In some cases, the antioxidant can be a phenyl group containing methoxy and/or hydroxyl substituents. In most of the illustrative compounds, however, a benzhydril moiety is coupled to the heterocycle simply through a CH group or C═ group. In the few compounds where there is an alkylene chain between the CH to which the two phenyl groups are bound and the heterocycle, the antioxidant must be coupled to the heterocycle through an unsubstituted alkylene and in most of these cases the antioxidant is a bicyclic system. Where the antioxidant can simply be a phenyl moiety coupled through an alkynylene, the linker from the heterocycle to the phenyl moieties contains no more than six atoms in the chain. U.S. Pat. No. 5,703,071 discloses compounds said to be useful in treating ischemic diseases. A mandatory portion of the molecule is a tropolone residue; among the substituents permitted are piperazine derivatives, including their benzhydril derivatives. U.S. Pat. No. 5,428,038 discloses compounds which are said to exert a neural protective and antiallergic effect. These compounds are coumarin derivatives which may include derivatives of piperazine and other six-membered heterocycles. A permitted substituent on the heterocycle is diphenylhydroxymethyl. Thus, approaches in the art for various indications which may involve calcium channel blocking activity have employed compounds which incidentally contain piperidine or piperazine moieties substituted with benzhydril but mandate additional substituents to maintain functionality.
Certain compounds containing both benzhydril moieties and piperidine or piperazine are known to be calcium channel antagonists and neuroleptic drugs. For example, Gould, R. J., et al., Proc Natl Acad Sci USA (1983) 80:5122–5125 describes antischizophrenic neuroleptic drugs such as lidoflazine, fluspirilene, pimozide, clopimozide, and penfluridol. It has also been shown that fluspirilene binds to sites on L-type calcium channels (King, V. K. et al. J Biol Chem (1989) 264:5633–5641) as well as blocking N-type calcium current (Grantham, C. J. et al. Brit J Pharmacol (1944) 111:483–488). In addition, Lomerizine, as developed by Kanebo KK, is a known calcium channel blocker; Lomerizine is, however, not specific for N-type channels. A review of publications concerning Lomerizine is found in Dooley, D., Current Opinion in CPNS Investigational Drugs (1999) 1:116–125.
In addition, benzhydril derivatives of piperidine and piperazine are described in PCT publication WO 00/01375 published 13 Jan. 2000 and incorporated herein by reference. This PCT publication corresponds to parent application Ser. No. 09/401,699 set forth above. Reference to this type of compound as known in the prior art is also made in WO 00/18402 published 6 Apr. 2000 and in Chiarini, A., et al., Bioorganic and Medicinal Chemistry, (1996) 4:1629–1635.
Various other piperidine or piperazine derivatives containing aryl substituents linked through nonaromatic linkers are described as calcium channel blockers in U.S. Pat. No. 5,292,726; WO 99/43658; Breitenbucher, J. G., et al., Tat Lett (1998) 39:1295–1298.
The present invention provides additional compounds which comprise benzhydril coupled to an acetyl group in turn coupled to a piperazine ring. The piperazine ring is, in turn, substituted by a variety of substituents, none of them antioxidants. These compounds are effective in blocking calcium ion channels.